DETERIORATION OF WATER QUALITY - THE EFFECTS ARISING FROM THE USE 0F FACTORY APPLIED CEMENT MORTAR LININGS (ESP 9770) FINAL REPORT TO THE DEPARTMENT OF THE ENVIRONMENT
Report No DWI0255

SEPT 1991

SUMMARY

I OBJECTIVES

  1. To identify and quantify the water quality problems caused by the use of factory applied, cement mortar lined, iron water mains;
  2. To provide guidelines on the limitations of application of factory applied cement mortar linings;
  3. To recommend methods for overcoming the potential water quality problems associated with the use of such linings.

II REASONS

In 1986, the Department of the Environment (DoE) commissioned WRc Plc to investigate the effect that in situ cement mortar lining had on water quality. These studies(1) showed conclusively that in situ lining of iron water mains in soft water supply regions can lead to pH, aluminium and lead levels which contravene the EC Directive(2) on potable water and the Water Supply (Water Quality) Regulations 1989.

The findings of this work led to concern that similar problems may be associated with factory applied cement mortar linings; the work reported in this document was commissioned by the Department of the Environment in April 1989 to investigate this.

III RESUME

A series of laboratory, full scale test-rig and field studies have been implemented in order to determine the effects of factory applied cement mortar linings on water quality.

Particular emphasis has been placed on the development of laboratory test-rigs which provide practical alternatives to costly full scale test-rig and field studies.

Data has been appraised in relation to previous in situ studies(l), and recommendations for use of factory linings have been developed.

IV CONCLUSIONS

  1. Factory applied linings are more satisfactory for use at lower alkalinities than in situ linings. In the case of 100 mm diameter pipes, and provided that retention time does not exceed 8 hours at any time, factory linings can be used when the supply water alkalinity is greater than 25mg CaCO3/l. At lower alkalinity levels leaching can cause pH levels to exceed the EC MAV and Water Act 1989 MAV of 9.5.
  2. When using cement mortar as a corrosion inhibitor for entire or large parts of distribution systems, the cumulative effect associated with long total retention times may result in pH in excess of 9.5 at the consumers tap. Very long retention times may result in high pH levels, even though the alkalinity is significantly greater than 25mg CaCO3/l.
  3. Seal coatings appear to provide an effective method of pH control; however, their long term durability and the potential for any water quality problems associated with such coatings have not been established.

V RECOMMENDATIONS

  1. Factory applied cement mortar lined pipes should not be used in conditions of very low alkalinity (less than 25mg CaCO3/l), where pipe diameters are small and retention times are relatively long. Caution should be exercised when considering the use of such linings when the total retention time is very high, even though the supply water alkalinity may be in excess of 25mg CaCO3/l.
  2. Theoretical extrapolation of the data should be used to provide an indication of the potential pH levels in a given defined system.
  3. The use of approved seal coatings, epoxy linings and other methods of preventing elevated pH should be considered in future investigations.
  4. Further field data should be collected to substantiate the findings of this work, which are mainly based on laboratory and test-rig data.
Copies of this report may be available as an Acrobat pdf download under the 'Pre 2000 Reports' heading on the DWI website.